To maintain the scroll position for the large web page you can use on of these methods :
1- use Web.config page section <pages maintainScrollPositionOnPostBack="true" />
: this will maintains the scroll positions for all the web site pages.
2- in the page declaration <%@ Page MaintainScrollPositionOnPostback="true" %> : this will maintains the scroll position for this page only.
3- programmatically from code behind System.Web.UI.Page.MaintainScrollPositionOnPostBack = true; : this will maintains the scroll position for this page only (the same as page declration).